Plenty of people still doubt that climate change is a real thing, or that it was engineered by humans and accelerating. But national security hawks agree with the scientific consensus that climate change is a real and growing problem. And they've done tons of research predicting the wars and disasters it could cause.

It shouldn't be too surprising that the United States military and intelligence community thinks of climate change as a national security threat. The 2014 Director of National Intelligence's "Worldwide Threat Assessment of the U.S. Intelligence Community" global threats included "Natural Resources" – divided up into the subcategories of Food, Water, Energy, Extreme Weather Events, and The Arctic. 2013's report was even more concerned openly about climate-based threats, using the term "climate change" more often, and giving the topic its own subheading.

One of the earliest available government reports on climate change as a national security threat is a 2003 report by the Pentagon Office of Net Assessments, which looked at an "abrupt climate change scenario." This, the Pentagon warned, could "de-stabilize the geo-political environment, leading to skirmishes, battles, and even
war."

The United States Joint Forces Command, which devoted a section to climate change in its 2007 report on trends and challenges they'd be facing through 2030. In this report, one concern was that climate change would exacerbate political instability and "foster the conditions for internal conflicts, extremism, and movement toward
increased authoritarianism and radical ideologies." Specifically, the report mentioned that climate change was a unique problem:

Unlike most conventional security threats characterized by the
activities of single entities acting in specific ways, climate change has the potential to result in
multiple chronic conditions, occurring globally within the same time frame.

This report built on the 2003's concern about increased military and humanitarian enagements, adding these threats to national security:

Effects may spread to
the U.S. Homeland in the form of refugee flows, internal weather-related disasters, energy
crises, and associated terrorist activities. Potential strategic implications may include the
potential opening of new sea lanes and access to new resources as a result of the melting
Arctic ice cap and tensions regarding availability or reallocation of energy resources. Climate
change may also have impacts on areas of military capability ranging from trafficability, to
potential inundation of military ports and other bases to sensor performance.

These aren't the only reports mentioning climate change from the early 2000s — what the reports all have in common is the U.S. military accepting that the problem is real, and expressing concerns about its effects.

Around this time, the United States intelligence community also became interested in the national security implications of climate change. This resulted in a 2008 National Intelligence Assessment (NIA) that was described as "the U.S. government's first analysis of the security threats posed by global warming." And this document was classified.

What is available is the statement made by the deputy director of national intelligence for analysis, to a joint House committee hearing. If the NIA was as the deputy director described it, it's somewhat strange that the report was classified. In fact, it was intended to be public — but was classified due to the fear that governments flagged in the report would react negatively. This seems like a futile gesture on the part of the government.

First, the deputy director's statement described the possible dangers faced by different regions, including specific countries. Second, the deputy director's statement made clear that they relied heavily on outside open sources and outside expertise. That means that it the information wasn't completely under the control of the government.

One of the groups consulted, Columbia University's Center for International Earth
Science Information Network actually published the results of what they were asked to do, which was to rank countries by looking at "sea-level rise, increased water scarcity, and an aggregate measure of vulnerability based on projected temperature change, compared with nations' ability to adapt."

The 2008 report was concerned with identifying the effects of climate change, and avoided the politically thorny questions about its cause or the validity of the science supporting it. Said the statement by Deputy Director Tom Fingar:

We did not evaluate the science of
climate change per se; nor did we independently analyze what the
underlying drivers of climate change are or to what degree climate change
will occur.

In 2011, the story of national security, climate change, and classified information gets a little weirder.

The CIA opened the Center on Climate Change and National Security in 2009. As with the 2008 report, the CIA claimed that the Center's aim wasn't to do scientific research on climate change, but to assess its impact on national security. (This did not stop the Center from drawing criticism.) The CIA's press release also charged the Center with figuring out what information and images captured by the intelligence community should be declassified and given to the scientific community to aid in their research. (Like the photos of Arctic ice loss, taken by spy satellites and also declassified in 2009.)

And yet, National Security Archive scholar Jeffrey Richelson's Freedom of Information Act request for "Any studies or reports (greater than 5 pages in length) produced by the
CIA Center on Climate Change and National Security concerning impacts of global
warming" was denied. In their response letter, the CIA stated:

We completed a thorough search for records responsive to your request and located
material that we determined is currently and properly classified and must be denied in its
entirety on the basis of FOIA exemptions (b)(l) and (b)(3). Exemption (b)(3) pertains to
information exempt from disclosure by statute. The relevant statute is the Central
Intelligence Agency Act of 1949, 50 U .S.C. § 403, as amended, e.g., Section 6, which
exempts from the disclosure requirement information pertaining to the organization,
functions, including those related to the protection of intelligence sources and methods,
names, official titles, salaries, and numbers of personnel employed by the Agency.

Which basically boiled down to the center declaring that there was no part of any report which could be declassified. Critics of the CIA's action pointed out that the fact that ice was vanishing and temperatures were increasing weren't secrets. At the time, Richelson told Wired:

As far as I know, they have not released any of their products or anything else. There was a statement announcing its creation and that has been pretty much it.

The CIA closed the office in 2012, to the approval of its critics in Congress. The CIA spokesperson made clear that it wouldn't stop monitoring the effects of climate change, just that it would no longer have a separate office for it. As the 2014 DNI report shows, climate change is still seen as a national security issue. Which raises the question about whether there are any more classified studies into it being made and whether climate change is an appropriate area for classification